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Integrated multi-trophic aquaculture has been considered as an alternative for the sustainable development of mariculture. This study evaluated the use of a multi-trophic system in mariculture in order to improve economic viability indices and reduce environmental impacts, leading to a sustainable production. To do so, the economic indicators of two monotrophic crops were considered: Perna perna mussels and Rachycentron canadum cobias, along with a multi-trophic system involving both species. The indices for the evaluation of profitability were the internal rate of return (IRR), the payback period (PP) and the net present value (NPV). Investment analyses were realized through cash flow and determination of economic viability indicators for a period of 10 years. The systems were evaluated in different scenarios. Each scenario was estimated by means of 20% and 40% variations of the values adopted for the following parameters: unit price of cobia juveniles, average price of the feed, cobia commercial price, mussel commercial price, cobia productivity, and mussel productivity. The multi-trophic system showed greater economic viability in the different scenarios evaluated. This system demonstrated greater resilience, which is more economically attractive to an entrepreneur. Production diversification is an alternative option with a lower associated investment, which can favor economic return and mitigate the risks of small-scale systems dedicated to monocultures.

Rachycentron canadum is an economically important fish in aquaculture due to its resistance to environmental variations, the feasibility of culture in confinement, high growth rates, and good acceptance by consumers. The profitability of their cage culture is negatively affected by the difficulty of implementing monosex cultures due to the apparent similarity between sexes. In this study, morphometric techniques were used to determine sexual dimorphism by analyzing measurements and the fish’s shape. Differences were found between the sexes in the position of the eyes, lips, pectoral fin and ventral fin, and the body’s general shape. The sexing precision of the individuals was 75.4 % with distances and 82.7 % with geometric morphometry. RESUMEN Rachycentron canadum es un pez con importancia económica en la acuacultura debido a su resistencia a variaciones ambientales, factibilidad de cultivo en confinamiento, altas tasas de crecimiento y buena aceptación de los consumidores. La rentabilidad de su cultivo en jaulas se ve afectada negativamente por la dificultad de implementar cultivos monosexo debido a la aparente semejanza entre los sexos. En este estudio se utilizaron técnicas morfométricas para determinar el dimorfismo sexual mediante el análisis de medidas y la forma de los peces. Se encontraron diferencias entre sexos en la posición de los ojos, labios, aleta pectoral y aleta ventral, y en la forma general del cuerpo. La precisión del sexado de los individuos fue de 75,4 % con distancias y 82,7 % con morfometría geométrica.

In the case of coinfections, multiple pathogens induce pathologies independently or in combination. The present study describes the pathological and microbiological characterization of Vibrio harveyi and two strains of Photobacterium damselae subsp. damselae causing coinfection in cobia reared in sea cages. All the isolated pathogens were virulent to juvenile cobia by injection challenge. The experimental challenge with the three isolated pathogens singly or in combination revealed a significant difference in the mortality profile. Lesions in natural coinfection consisted of ascites, fibrinous deposits on internal organs, and increased melanomacrophage centres (MMC) and extensive necrosis in kidneys. Lesions in experimental infection were limited to congestion of internal organs. Enzymatic activity of both extracellular products (ECP) and live cells by well diffusion showed the highest enzymatic index for gelatinase in the ECP of V. harveyi. The enzyme activity evaluated based on the API‐ZYM system revealed the highest activity for alkaline and acid phosphatase in both ECP and bacteria. The MAR index indicated that the pathogens were from a low‐risk region of antibiotic contamination.

The heme oxygenase gene plays a role in many biological processes and is an important protective factor in hypoxic stress. Research on the HO gene of fishes has attracted increasing attention, but there is yet little information about the cobia (Rachycentron canadum) heme oxygenase gene. In this study, the full-length cDNA of the cobia heme oxygenase gene (heme oxygenase, HO) was cloned using rapid amplification of cDNA ends technology. The full-length cDNA was 1639 bp and the open reading frame (ORF) was 840 bp encoding 279 amino acids, with 5′-UTR 518 bp and 3′-UTR 281 bp. The results of real-time quantitative PCR showed that cobia HO was expressed in all the tissues tested, with the highest expression in gills. The mRNA expression of gill HO increased after hypoxia stress. There was no significant change in the expression of HO mRNA in the liver after hypoxia stress. The amino acid sequences of HO in diverse fish and mammals have varying levels of homology. Our results indicate that the biological functions of HO may be similar in fish and mammals, suggesting an important protective factor in response to hypoxic stress.

Juvenile cobia (Rachycentron canadum), a carnivorous fish, was chosen to examine the effects of methionine (Met) supplementation of low fishmeal diets on growth and the expression of key genes related to hepatic lipogenesis and glucose metabolism. Seven isonitrogenous and isolipidic diets were formulated to contain 7.2, 9.0, 10.0, 12.4, 14.1, 16.3 and 18.6 g/kg dietary Met levels. Healthy cobia (initial average weight ± SE = 9.79 ± 0.04 g) were randomly assigned into seven groups in triplicate with 40 individuals per sea cage for 8 weeks. The results showed that the weight gain rate (WGR) of fish increased as the dietary Met was increased up to 12.4 g/kg and then decreased. The expression of insulin‐like growth factor‐I (IGF‐I) and target of rapamycin (TOR) genes was inhibited by the Met‐deficient diets. The mRNA levels of fatty acid synthase (FAS) and sterol regulatory element‐binding protein‐1 (SREBP1) genes increased with increasing dietary Met until 12.4 g/kg after which the former remained constant, whereas the latter decreased from 12.4 to 18.6 g/kg Met. The mRNA levels of pyruvate kinase (PK) increased as the dietary Met levels increased, reaching a peak at 12.4 g/kg, and then decreased with further increases in Met. However, the mRNA levels of phosphoenolpyruvate carboxykinase (PEPCK) decreased as the dietary Met was increased up to 12.4 g/kg and then remained constant from 12.4 to 18.6 g/kg Met. In conclusion, based on the straight broken‐line analysis of WGR against dietary Met levels, the optimal dietary Met requirement for juvenile cobia was estimated to be 12.4 g/kg (26.9 g/kg dietary protein). A diet with the optimal level of Met induces fish growth and is associated with increased IGF‐I and TOR.

The effects of dietary k-Carrageenan (k-CGN) at 10, 20, and 30 g kg−1 on growth rate, hemato-biochemical indices, innate-adaptive parameters and modification of pro- and/or anti-inflammatory cytokines and chemokines pathway in cobia, Rachycentron canadum against Lactococcus garvieae is reported. The weight gain (WG) increased substantially (P

Cobia (Rachycentron canadum) is an important cultured marine fish species in southern China. It is characterized by fast growth. Due to the effects of climate change on water oxygen levels and seawater temperatures, the understanding of the influence of environmental changes on cobia culture has become important. In this study, to explore the stress and adaptability of cobia under hypoxia-reoxygenation conditions, the fish were exposed to an oxygen-deficient environment with dissolved oxygen (DO) level of 2.64 ± 0.25 mg/L. Serum liver function target, lipid metabolism-related enzymes and the serum antioxidant capability were detected in cobia under acute hypoxic stress after which fish returned to normal DO level (6.34 ± 0.15 mg/L) at 8, 24 and 48 h. Conventional paraffin sectioning and hematoxylin and eosin (H-E) staining were used to observe gill and liver tissues of cobia by electron microscopy. After hypoxic stress, the activities of alkaline phosphatase (ALP), total protein (TP), albumin (ALB), triglyceride (TG), total cholesterol (TC) and superoxide dismutase (SOD) in cobia decreased. Under acute hypoxic stress, the gill patches of the fish were contracted and slightly curved. Liver disorder and vacuoles appeared between liver tissues. After reoxygenation, SOD and catalase (CAT) were recovered to the level of the control group with time, and all peaks appeared. The gill and liver of fish were also recovered with time. The results showed that hypoxic stress could cause oxidative damage to cobia.

Large-scale fish farming faces many environmental stresses, which affect their immune systems, growth performance, and physiological homeostasis, resulting in increase in their susceptibility to infections. Some of the most common bacterial infections of cobia fish (Rachycentron canadum) include streptococcosis, vibriosis, furunculosis and mycobacteriosis, and pastelleurosis. Probiotics could be helpful in reducing or limiting the incidence of severe disease infections or outbreaks. Therefore, the present study aimed to isolate the indigenous bacterial species from healthy cobia fish and then selected 3 strains, including Bacillus sp. RCS1 (MW560712), Pantoea agglomerans RCS2 (MW560713), and Bacillus cereus RCS3 (MW560714) from the gut of juvenile’s cobia having advantageous assets or positive characteristics. Their analysis indicated the presence of similar biochemical profiles and all could effectively utilize carbon sources. The biosafety assessment did not show any pathological symptoms after 10 days of injecting the fish with isolated bacteria. The results showed that all the isolated bacteria in the present study had low auto-aggregation capacity within the first 3 h of incubation. The isolated bacteria showed strong tolerance when exposed to a range of pH. Although asymmetrically, a slow rise in the growth of isolated bacteria was observed within the pH range of 1–8 for RC1, 1–7 for RC2, and 1–6 for RC3. The antagonistic effects of isolated bacterial strains on the development of pathogens, including Vibrio alginolyticus, Vibrio harveyi, Streptococcus iniae, and Streptococcus agalactiae, were investigated using Luria-Bertani (LB) agar plates. All the isolated bacteria exhibited inhibitory effects against the pathogens, including V. alginolyticus, V. harveyi, S. iniae, and S. agalactiae. These isolated bacteria were characterized with a wide range of antagonistic activities, non-hemolytic activities, high survivability after heat-treatments and safety confidence, and antibiotic susceptibility. Generally, the characteristics displayed by these strains indicated that they could be used as potential probiotics in the aquaculture industry.

The present study reports the first incidence of intersex in Cobia, Rachycentron canadum maintained at sea cages in the Gulf of Mannar, India. During the 10 year study period (2010–2019), at total of 815 broodstock (386 wild captured and 429 captive raised) were maintained under captivity in sea cages in the Gulf of Mannar, India for the purpose of seed production. Of which, 318 male and 252 female broods’ gonads were examined post-mortem following a natural death. Only one male fish was found with a visible gonadal anomaly. Microscopic analysis of gonad revealed the presence of both the characteristic female and male tissues in testes of a single specimen (testis-ova). Only the abnormal nodular portion contained primary oocytes, whereas the central testicular tissue contained spermatocytes and spermatids in the seminiferous lobules. This is the first reported intersex of cobia from the Gulf of Mannar, India. It could be interpreted as low-level rare incidence of natural aberration.

At present, due to the influence of global warming, seasonal change, diurnal variation, and eutrophication of the water body, hypoxia has become one of the major factors limiting the stable development of cobia (Rachycentron canadum) culture. In this study, the miRNAs involved in hypoxia stress were screened, and the target genes of miRNAs were annotated and analyzed. The results showed that a total of 184 conservative microRNA (miRNA) and 121 newly predicted miRNA were obtained by sequencing the liver of control (C) and hypoxic (dissolved oxygen, DO (2.64 ± 0.25) mg/L; 3 h) (S) groups. The pathways involved in energy metabolism included starch and sucrose metabolism (ko00500), glycosaminoglycan degradation (ko00531), and galactose metabolism (ko00052). The results indicate that the body maintains physiological activities by regulating some important pathways at the transcriptional level under hypoxia stress, such as the conversion of aerobic metabolism and anaerobic metabolism, the reduction of energy consumption, and the promotion of red blood cell proliferation to maintain the homeostasis of the body.

Made available in DSpace on 2021-06-25T15:07:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-08-30 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Centro de Biologia Marinha da Universidade de Sao Paulo (CEBIMar) This study aimed to investigate the influences of alternative lipid sources rich in saturated and monounsaturated fatty acids (SFA and MUFA) supplemented with long-chain polyunsaturated fatty acids (LC-PUFA) on production performance and lipid metabolism of Rachycentron canadum (cobia) juveniles. An 8-week feeding trial was carried out using four isoproteic and isolipidic diets as follows: FO-D (fish oil, as control diet), SFA-D (rich in SFA), MIX-D (same levels of SFA and MUFA), and MUFA-D (rich in MUFA). Experimental diets were supplemented with arachidonic acid (ARA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) (3, 5, and 10 g kg(1), respectively). The growth performance, fatty acid (FA) profile of liver and muscle, hepatocyte morphology, and gene expression related to the FA synthesis and oxidation on the liver were examined. In general, production performance was not impaired in fish-fed FO-free diets, supporting the hypothesis that alternative lipid sources could be used in cobia's aquafeed formulations when the LC-PUFA are adequately supplemented. High dietary SFA levels were disproportionally deposited the liver and muscle. Contrariwise MUFA was mainly deposited in the liver and muscle, reflecting the dietary inclusion levels. The main FA influencing this pattern were 12:0 and 18:1n-9. The expression of fatty acid synthase (fas) was up-regulated in the FO-D group compared to SFA-D and MIX-D groups. There were no differences in the relative expressions of carnitine palmitoyltransferase 1 (cpt-1 alpha) and lipase lipoprotein (lpl). The liver morphology results indicated that fish-fed SFA-D presented a smaller lipid vacuoles area than those fed other experimental diets. This study shows that SFA with shorter carbon chains such as 12:0 can be administered in cobia aquafeeds to stimulate these molecules' catabolism, providing energy for growth, and retaining LC-PUFAs in tissues, especially in the muscle, exhibiting a healthier fillet for consumers. Univ Sao Paulo, Dept Fisiol, Inst Biociencias, Rua Matao,Trav 14,321, BR-05508090 Sao Paulo, SP, Brazil Univ Sao Paulo CEBIMar USP, Ctr Biol Marinha, Rodovia Manoel Hipolito Rego,Km 131,5, BR-11612109 Sao Sebastiao, SP, Brazil CSIRO Agr & Food, Livestock & Aquaculture Program, Bribie Isl Res Ctr, Woorim, Qld 4507, Australia Univ Autonoma Baja California UABC, Inst Invest Oceanol, Km 107 Carretera Tij Eda, Ensenada 22860, Baja California, Mexico Univ Estadual Paulista Julio de Mesquita Filho CA, Ctr Aquicultura, Via Acesso Prof Paulo Donato Castellane S-N, BR-14884900 Jaboticabal, SP, Brazil UABC, Inst Invest Oceanol, CONACYT, Ensenada, BC, Mexico Univ Mogi das Cruzes, Nucleo Integrado Biotecnol, Ave Dr Candido Xavier Almeida Souza 200, BR-08780911 Mogi Das Cruzes, SP, Brazil Univ Estadual Paulista Julio de Mesquita Filho CA, Ctr Aquicultura, Via Acesso Prof Paulo Donato Castellane S-N, BR-14884900 Jaboticabal, SP, Brazil FAPESP: 2019/092469 FAPESP: 2014/163207 FAPESP: 2017/067650 FAPESP: 2019/260180

Cobia (Rachycentron canadum) is a large coastal pelagic fish species that represents an important fishery in many coastal Atlantic states of the U.S. They are heavily fished in Virginia when they migrate into Chesapeake Bay during the summer to spawn and feed. These coastal habitats have been subjected to warming and increased hypoxia which in turn could impact the timing of migration and the habitat suitability of Chesapeake Bay. With conditions expected to worsen, we project current and future habitat suitability of Chesapeake Bay for cobia and predict changes in their arrival and departure times as conditions shift. To do this we developed a depth integrated habitat model from archival tagging and physiology data from cobia that used Chesapeake Bay, and applied the model to contemporary and future temperature and oxygen output from a coupled hydrodynamic-biogeochemical model of Chesapeake Bay. We found that estimated arrival occurs earlier and estimated departure time occurs later when temperatures are warmer and that by mid- and end-of-century cobia may spend on average up to 30 and 65 more days, respectively, in Chesapeake Bay. By mid-century we do not expect habitat suitability to change substantially for cobia, but by end-of-century we project it will significantly decline and shift closer to the mouth of Chesapeake Bay. Our study provides evidence that cobia will have the capacity to withstand near term impacts of climate change, but that their migration phenology varies from year to year with changing temperatures. These findings emphasize the need to incorporate the relationship between fishes and their environment into how fisheries are managed. This information can also help guide managers when deciding the timing and allocation of a fishery.

Insulin-responsive glucose transporter 4 (GLUT4), a member of the glucose transporter family, plays a vital role in mediating glucose movement across cell membranes in insulin-sensitive tissues. In this study, we aimed to compare the molecular characterization and expression analysis of GLUT4 from three fish species of different feeding habits: golden pompano (Trachinotus ovatus), cobia (Rachycentron canadum) and tilapia (Oreochromis niloticus) after being fed three different dietary carbohydrate-to-lipid (CHO:L) ratios for 8 weeks. The results showed that the full length of golden pompano GLUT4 (ToGLUT4) and cobia GLUT4 (RcGLUT4) gene cDNA are 1973 and 2241 bp, containing an open reading frame (ORF) encoding 506 and 507 amino acids, respectively. Sequence alignment and phylogenetic analysis of GLUT4 revealed a high degree of conservation among most fish and higher vertebrates, and high homology were found in GLUT4 of golden pompano, cobia and tilapia, which share several identical motifs but contain small substitutions in GLUT4 protein. In addition, the highest GLUT4 gene expression was observed in white muscle followed by heart in these three fish species. Furthermore, in all these three species, the expression of GLUT4 was regulated in heart and white muscle by dietary CHO:L ratios. Expression of GLUT4 in heart decreased when golden pompano and tilapia were fed medium or high CHO:L ratio diets. However, in cobia, GLUT4 was induced when fed medium CHO:L ratio diet but depressed when fed high CHO:L ratio diet. With respect to white muscle, high expression of GLUT4 was found in these three fish species when fed medium CHO:L ratio diet, and high CHO:L ratio diet intake depressed its abundance in white muscle. The results indicate that GLUT4 of golden pompano, cobia and tilapia share several functionally important structural characteristics but contain small substitutions in GLUT4 protein that may lead to differences in the traffic behavior and affect the efficiency of glucose transport. In accordance with mammalian expression pattern, GLUT4 of golden pompano, cobia and tilapia are all expressed primarily in heart and white muscle, which could be regulated by dietary CHO:L ratios but appear to be species-specific and tissue-specific. However, none of the parameters examined clarifies the differences in carbohydrate utilization between carnivorous (golden pompano, cobia) and omnivorous (tilapia) fish. Decreased GLUT4 mRNA in heart and white muscle caused by feeding a relatively high carbohydrate with low lipid diet might partially explain the poor utilization of carbohydrate in these three fish species.

This study investigates the effects of three medicinal herbal extracts, namely Bidens pilosa (BPE), Lonicera japonica (LJE), and Cyathula officinalis (COE), on nonspecific immune parameters of cobia (Rachycentron canadum) in vitro and in vivo. During in vitro tests, BPE treatment increased reactive oxygen species (ROS) production in a dose-dependent manner in primary head kidney leukocytes. Similarly, ROS production rates were enhanced by LJE (50 and 100 mg/ml) and COE (100 mg/ml). This suggests that these three herbal extracts possess immunostimulating properties. We then conducted two feeding trials to examine the effects of these three herbal extracts on growth and innate immune parameters of cobia, and sought an optimal dietary supplementation proportion required for activating the non-specific immune responses. In the first trial, we supplemented the diet with 1, 5, or 10% of the individual extracts. After a ten-week feeding trial, no negative impacts on weight gain, feed conversion rate, and survival rate were observed in fish offered experimental diets. Further, ROS production, phagocytic capacity of the head kidney leukocytes, and serum lysozyme activity were enhanced by differing degrees in fish fed the herbal extracts compared to fish in the control group. A similar albumin/globulin ratio was seen between each experimental group and the control group regardless of the type and dose of herbal extract used, indicating these medicinal herbal extracts are safe for cobia. We then performed a 30-day feeding trial with lower extract concentrations (1, 3, and 5% of the diet) to identify dose responses in cobia at various time points so that we could establish a cost-effective manner of administering the three extracts for cobia. All BPE fed fish had higher ROS production compared to the control group, while phagocytosis rate and index were simultaneously raised in only the BPE30 group (3% BPE). Immune parameters such as ROS production, phagocytic rate, and serum lysozyme activity were triggered when fish received 30 g LJE per kg of feed. However, ROS production only increased in the LJE10 group (1% LJE) on day 30 and was not enhanced in the LJE50 group (5% LJE). Additionally, although the phagocytic rate and phagocytic index were induced in the LJE50 group, serum lysozyme activity was not elevated in this group (LJE50) at any time point examined. ROS production was greatly improved in all COE fed groups, but only the COE30 group (3% COE) showed prolonged enhanced phagocytic rate over the 30-day feeding trial.

Three studies were conducted with juvenile cobia, Rachycentron canadum: (Study 1) a 10‐week feeding trial within floating net cages to test the nutritional efficacy of different dietary feeding regimes (trash‐fish control diet, a semimoist diet, an in‐house dry formulated diet, and a commercial cobia feed); (Study 2) a 10‐week feeding trial within an indoor water‐recirculating tank‐based system to test the nutritional efficiency of different potential dietary fishmeal replacers (poultry byproduct meal, soy protein concentrate, feather meal), a diet without taurine supplementation, and a commercial cobia feed; and (Study 3) estimation of the essential amino acid (EAA) requirements of cobia based on EAA whole‐body composition in fast‐growing cobia fed a trash‐fish‐based diet. Fish performance in terms of growth and feed efficiency was the greatest within the outdoor net‐cage feeding trial, with fish fed the control trash‐fish‐based diet exhibiting the best performance. Although fish growth was poorer within the indoor feeding trials, fish performance was similar for most diets, with apparent crude protein digestibility coefficients of over 75% being obtained in all experimental diets in both feeding trials. The estimated EAA requirements of cobia obtained during this study were similar to those reported for other similar marine carnivorous fish species.

Rachycentron canadum (cobia) is a species that has attracted the interest of the marine fish farming industry due to displaying numerous traits favorable to cultivation. The species is characterized by its large size, rapid growth, robustness and established technological support for cultivation. Cobia shows sexual size dimorphism (SSD) as adults, with females being significantly larger than males. In fish, sexual dimorphism related to morphology can be the result of ecological, functional, or adaptive selection. Methodologies that allow the application of monosex cultures increase both the biotechnological and production potential of a species. With a view to establishing parameters for early sex determination in R. canadum, morphological analyses were conducted in juveniles aged 139 days (4.6 months) using geometric morphometrics. Sexual shape dimorphism (SShD) in female cobia is expressed by an elongated body and extended space between pectoral and anal fins, suggesting fecundity-related morphological adaptations. The results are promising and indicate a high index of early sex discrimination using geometric morphometrics, demonstrating the possibility of developing routine protocols that can be applied to increase species production.

Streptococcus dysgalactiae is a major concern in cobia (Rachycentron canadum) cultured in Taiwan; however, there have been no reports on vaccines against this pathogen. This study considered the immune response and protective efficacies of a S. dysgalactiae-derived inactivated vaccine in this fish species. Streptococcus dysgalactiae isolate SD49, belonging to the predominant PFGE pulsotype S1A1, in which 86% of isolates have been classified and SD12 being the highest virulent strain were two vaccine candidates chosen for this study. The bacterin vaccine using a mixture of these two isolates was safe and immunized fish induced greater lysozyme, phagocytosis activities, and antibody responses. Notably, the vaccine protected cobia from the highest virulent S. dysgalactiae strain with a 100% relative percentage survival when challenged 6 weeks post primary vaccination. Together, the divalent vaccine could stimulate immune responses and effectively protect cobia against S. dysgalactiae infection.

The immune responses and protection efficacy of a vaccine containing inactivated formalin-killed Photobacterium damselae subsp. piscicida formulated with alum and different unmethylated Cytosine phosphorothioate Guanine oligodeoxynucleotides (CpG-ODN, including 2006, 2395, 1668, and control ODN 2137) as the adjuvant were investigated in cobia Rachycentron canadum. Results showed that, formulation with CpG-ODN 1668 significantly (P

This study investigated the efficacy of the aqueous fraction obtained after fractionating silage of tilapia (Oreochromis niloticus) and cobia (Rachycentron canadum) in supporting the growth of Escherichia coli and Staphylococcus aureus. The silages were prepared using combinations of citric, formic, and propionic acids. The aqueous fractions, used as test peptones, contained lower levels of total protein. The concentrations of 18 amino acids in all the samples were observed to be lower than those in the commercial peptone. Glutamic acid, lysine, glycine, and aspartic acid were present in higher concentrations than other amino acids, for both types of silage. Biomass production from E. coli culture ranged from 38.4 to 65.9 mg 100 mL−1 for all the tested treatments, while that for S. aureus was from 26.3 to 53.7 mg 100 mL−1. This indicated that products from fish silage were effective for bacterial growth in terms of biomass, by providing the main sources of nitrogen and carbon to facilitate their growth. The tested silages yielded similar efficiency to the commercial peptone. The findings revealed that it is feasible for the fish processing industry to incorporate freeze-dried by-products obtained after fractioning waste silage from the processing of tilapia and cobia. © 2018, © 2018 Taylor & Francis. The authors thank the Coordination for the Improvement of Higher Education Personnel (CAPES – Coordination for the Improvement of Higher Education Personnel – Case no. 23038.051665/2009-04), São Paulo Research Foundation (FAPESP – São Paulo Research Foundation – Case no. 2013/13158-1), and National Council for Scientific and Technological Development (CNPq – National Council for Scientific and Technological Development – Case no. 482619/2013-9) for the scholarship and financial support.

Cobia, Rachycentron canadum is a candidate species for aquaculture, distributed across the Indo-Pacific waters to the southern Atlantic Ocean. Information on genetic diversity and population structure of cobia is crucial for sustainable utilization and management of the species in natural waters. In the present study, we used 14 polymorphic microsatellite loci and mitochondrial cytochrome b gene (980 bp) to investigate the genetic diversity and population structuring of R. canadum along the Indian coast. Microsatellite analysis suggests a relatively high level of genetic diversity of cobia in the Indian region, with a mean Ho and He of 0.76 and 0.73. The PIC was also highly informative (0.841), with a mean no. of alleles of 11.304. Hierarchical AMOVA and genetic differentiation co-efficient between the populations was found to be low, but significant (FST = 0.035, P

Tumor necrosis factor-alpha (TNF-α) and interleukin-8 (IL-8/CXCL8) play pivotal roles in mediating inflammatory responses to invading pathogens. In this study, we identified and analyzed expressions of cobia TNF-α and IL-8 during Streptococcus dysgalactiae infection. The cloned cDNA transcript of cobia TNF-α comprised of 1281 base pairs (bp), with a 774 bp open reading frame (ORF) encoding 257 amino acids. The deduced amino acid sequence of cobia TNF-α showed a close relationship (84% similarity) with TNF-α of yellowtail amberjack. The cloned IL-8 cDNA sequence was 828 bp long, including a 300-bp ORF encoding 99 amino acids. The deduced amino acid sequence of cobia IL-8 shared 90% identity with IL-8 of striped trumpeter. Cobia challenged with a virulent S. dysgalactiae strain displayed an early significant up-regulation of TNF-α and IL-8 in head kidney, liver, and spleen. Notably, IL-8 expression level increased dramatically in the liver at the severe stage of infection (72 h). In conclusion, a better understanding of TNF-α and IL-8 allows more detailed investigation of immune responses in cobia and furthers study on controlling the infectious disease caused by S. dysgalactiae.

Severe clinical mycobacteriosis with consistent ocular lesion localization was diagnosed in a population of 800 juvenile tank-reared Cobia (Rachycentron canadum) which experienced a sudden increase in mortality approximately 5 months after arriving into Trinidad and Tobago from Florida, USA. Moderate daily mortality (15-20 animals per day) persisted for just over 1 month. Moribund fish displayed circling behaviour and had an open-mouth gape upon death. Fish consistently presented with bilateral exophthalmia, corneal cloudiness and hyphema. Non-branching acid-fast rods were detected in aqueous humour touch preparations. Histological analysis revealed severe bilateral intra-ocular granulomatous responses in all specimens. Mycobacterium sp. was identified using a real-time PCR assay detecting the RNA polymerase β-subunit (rpoB) gene in different tissue samples. Specimens did not present with characteristic granulomatous responses usually seen in viscera. To the best of our knowledge, this represents only the third documentation of piscine mycobacterial infection presenting with only localized ocular lesions, and the second documented case of mycobacteriosis in cobia. It is, however, the first documentation of an ocular presentation of mycobacteriosis in a marine species and is the first documentation of such a presentation in cobia.

Ongoing global warming is one of the major challenges for the development of aquaculture in the tropical regions where species are already cultured in the water temperature close to their upper physiological thresholds. Furthermore, warming can trigger blooms of toxic algae, yet we do not know how extreme warming such as a marine heatwave (MHW) and algal toxins may affect marine aquaculture species. To address this issue, we investigated the effects of a simulated MHW in combination with exposure to trans-4-trans-decadienal (PUA), a diatom-derived toxin, on survival, growth, development and biochemical composition of cobia larvae and juveniles. Cobia larvae were exposed for 48 hr to one of two temperatures (29 vs. 34°C) and two PUA treatments (0 vs. 0.5 µM). Surviving larvae from each treatment were divided into two subsets: three replicates were used for the feeding test and five replicates were used for the recovery test in a non-contaminated environment at the respective temperatures of 29 or 34°C. Survival of cobia larvae was reduced by 16% in either MHW or PUA, but it dropped by 60% when both stressors were present, indicating a synergistic effect. MHW, but not PUA, reduced the feeding of cobia larvae. PUA had no delayed effects on growth rate and biochemical composition of the fish. MHW strongly reduced specific growth rate, body protein and lipid contents in cobia. Our results provide the first empirical evidence of how MHW and toxic algae may interact and challenge cobia and marine aquaculture production in tropical countries. publishedVersion

The co-receptor CD4 plays an important role in distinguishing between helper T-cell (Th) and cytotoxic T lymphocyte (CTL). In the present study, we investigated the molecular features of CD4-2 cDNA to facilitate understanding of their roles in cobia (Rachycentron canadum). Two CD4-2 molecules have been identified and exhibited 16.10% amino acids identity with each other. The cDNA of CD4-2A consists of a 993 bp ORF encoding 330 aa with long intracytoplasmic tail containing conserved protein tyrosine kinase p56Lck binding (C-X-C) motif, a transmembrane region, and two extracellular Ig-like (Ig-like) domains are predicted. Comparatively, the cDNA of cobia CD4-2B consists of a 990 bp ORF encoding 329 aa without a transmembrane domain as well as C-X-C motif, and three Ig-like domains are present. Homology comparison showed that the CD4-2A aa sequence of cobia showed high similarity and similar structural features to CD4-2 from other species, while the deduced CD4-2B protein shares higher structural similarity to CD4-1 group. Phylogenetic analysis indicated that cobia CD4-2A was closer with CD4-2 molecules in other fish species, distant from the clade formed by fish CD4-1 and mammalian CD4 sequences. However, cobia CD4-2B grouped with other known teleost CD4-1 sequences. The expression pattern of CD4-2A and CD4-2B mRNA during the embryonic development followed the trend of an initial increase after fertilized, providing evidence of maternal transfer of CD4-2 homologues to the developing cobia embryos and larvae. All of these results are useful for better understanding of cell-mediated immunity of cobia.

An innovative aquaculture project involving the thermal seawater effluent of a thermoelectric power plant and a recirculating aquaculture system (RAS) was implemented in the Atacama Desert, the driest in the world located in northern Chile to produce the warm water pelagic fish cobia (Rachycentron canadum Linnaeus, 1766). An experimental land-based fish farm was built consisting of nine independent RAS provided with adequate temperature (28°C) and salinity (32) for cobia growth and overall aquaculture performance. Under these conditions, cobia was raised from egg to an average weight of 4 ± 0.4 kg in 12 months. Growth rates were similarly high for all the batches, and mortalities from weaning up to harvest sizes never exceeded 6%. Besides, no antibiotics were ever used, and no infectious diseases ever detected during the four years experimental phase reported herein. The batches of eggs arrived in Chile in 2012 and 2014. After three years, 12 t of cobia were consistently produced per every eight months’ cycle. During this period, successful reproduction and routine volitional spawning of broodstock were achieved, producing offspring from F1 and F2 generations. The biological potential and economic feasibility of the RAS concept for raising cobia in temperate, desert regions was demonstrated and is described. Farm management, multi-trophic aquaculture, animal welfare, proactive health management, zero water effluent discharge, and total recycling of wastes are also discussed as a means of expanding the concept into a commercial phase.

Salinity is an important abiotic stress that affects metabolic and physiological activities, breed, development, and growth of marine fish. Studies have shown that cobia (Rachycentron canadum), a euryhaline marine teleost fish, possesses the ability of rapid and effective hyper/hypo iono- and osmoregulation. However, genomic studies on this species are lacking and it has not been studied at the transcriptome level to identify the genes responsible for salinity regulation, which affects the understanding of the fundamental mechanism underlying adaptation to fluctuations in salinity. To describe the molecular response of cobia to different salinity levels, we used RNA-seq analysis to identify genes and biological processes involved in response to salinity changes. In the present study, 395,080,114 clean reads were generated and then assembled into 65,318 unigenes with an N50 size of 2758 bp. There were 20,671 significantly differentially expressed genes (DEGs) including 8805 genes adapted to hypo-salinity and 11,866 genes adapted to hyper-salinity. These DEGs were highly represented in steroid biosynthesis, unsaturated fatty acid metabolism, glutathione metabolism, energy metabolism, osmoregulation, and immune response. The candidate genes identified in cobia provide valuable information for studying the molecular mechanism of salinity adaptation in marine fish. Furthermore, the transcriptomic sequencing data acts not only as an important resource for the identification of novel genes but also for further investigations regarding cobia biology.

The ICAR-Central Marine Fisheries Research Institute (ICAR-CMFRI) is the pioneer in developing the technology for cage fish farming in India . Cobia (Rachycentron canadum) grows relatively fast in cages and is very much suited for carrying out small scale mariculture to meet the alternate livelihood needs of fisher-folk. Mandapam Regional Centre of ICAR-CMFRI has developed the technology for breeding, seed production and farming of cobia in cages and organised training, and frontline/participatory demonstration programmes which have aided in creating awareness about the techno-economic viability of cage farming among the fisherfolk in Ramanathapuram District, Tamil Nadu. A survey was taken up among a sample of 75 members of fisher self help groups (SHGs) who had adopted cage farming of cobia, inorder to assess their perception and attributes about the technology as well as the constraints faced by them. The study found that fast growth rate of cobia, shorter culture period, good farm gate price, high market demand, ease of farming near the seashore and seed availability were the important attributes which attracted the fishermen groups to take up the farming. The innovations introduced by the fishers in cage farming technology were also documented. Majority of the fishers stated, non-availability of seed during peak stocking season, high cost of pellet feed, fluctuating cost of low value fishes which are used as feed for cobia and poaching as major constraints in cage farming.

Made available in DSpace on 2019-10-04T12:40:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-09-15 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) An 8-week nutritional experiment was conducted with the aim of evaluating the influences of different arachidonic acid (ARA) levels and two different temperatures (29.5 degrees C and 26.5 degrees C) on the growth performance, tissue and whole-body fatty acid (FA) compositions, plasma prostaglandin concentration, liver morphology and expression of genes related to lipid metabolism in cobia juveniles. A basal fat-reduced diet was manufactured and subsequently coated with different FA sources, distinct levels of ARA (ARA1, 0.5%; ARA2, 1.2%; and ARA3, 1.9%) and fish oil (FO: 8.8%, as a control diet). All diets were formulated to be isoproteic and isolipidic. Cobia juveniles (5.86 +/- 0.40 g) were randomly divided into 24 tanks with 18 animals each. Twelve tanks were kept at 29.5 degrees C, and 12 tanks were kept at 26.5 degrees C. The animals were fed twice per day with each experimental diet until apparent satiation in triplicate tanks at both temperatures. The results revealed that the animals maintained at 26.5 degrees C and fed with the ARA diets exhibited better growth than those fed with the FO diet and kept at 29.5 degrees C. In contrast to observations in other teleost species, ARA excess did not reduce growth or survival. The FA compositions of the livers, fillets and whole bodies generally reflected the diet compositions, i.e., gradual increases in ARA were observed according to the diet level. Additionally, greater depositions of docosahexaenoic acid (DHA) in the fillets of the animals from the ARA2 group that was kept at 26.5 degrees C were observed. The plasma prostaglandin levels were greater in the animals that were kept at 29.5 degrees C for all experimental diets and in the ARA2 animals compared with the FO groups at both temperatures. The FAS and SREBP-1 expressions in the livers were down-regulated in the ARA1 and ARA2 animals that were maintained at 26.5 degrees C compared with the animals that were fed the same diets but kept at 29.5 degrees C. Additionally, SREBP-1 expression was up-regulated in the ARA2 animals compared with the FO animals at both temperatures. The results of this study indicated that ARA inclusion between 0.5 and 1.9% combined with a temperature of 26.5 degrees C can improve juvenile cobia growth performance and directly influence the modulation of prostaglandin synthesis and the relative expressions of lipid genes. Univ Mogi das Cruzes, Nucl Integrado Biotecnol, Av Dr Candido Xavier de Almeida Souza 200, BR-08780911 Mogi Das Cruzes, SP, Brazil Univ Sao Paulo CEBIMar USP, Ctr Biol Marinha, Rodovia Manoel Hipolito Rego Km 131,5, BR-11600000 Sao Sebastiao, SP, Brazil CSIRO, Agr & Food, Aquaculture Program, Bribie Isl Res Ctr, Woorim, Qld 4507, Australia Univ Estadual Paulista Julio de Mesquita Filho CA, Ctr Aquicultura, Via Acesso Prof Paulo Donato Castellane S-N, BR-14884900 Jaboticabal, SP, Brazil Univ Sao Paulo, Inst Biociencias, Dept Fisiol, Rua Matao,Trav 14,321, BR-05508090 Sao Paulo, SP, Brazil Univ Estadual Paulista Julio de Mesquita Filho CA, Ctr Aquicultura, Via Acesso Prof Paulo Donato Castellane S-N, BR-14884900 Jaboticabal, SP, Brazil FAPESP: 2014/16320-7 FAPESP: 2016/12435-0

Streptococcus dysgalactiae is an important pathogenic bacterium that has caused economic loss for the cobia industry in Taiwan, ROC. This study presents a highly effective subunit vaccine composed of a moonlight protein, α-enolase, for the prevention of S. dysgalactiae infection. First, α-enolase was cloned, transformed, and expressed in E. coli for production of recombinant protein. Then, the protective efficacies of α-enolase recombinant protein were evaluated in combination with either a pro-inflammatory cytokine, TNF-α, or an oil adjuvant, ISA 763 AVG. The results showed that the combination of α-enolase and ISA 763 AVG was highly protective (RPS = 88.89%), while a negative effect was found in the group immunised with α-enolase adjuvanted with TNF-α (RPS = 22.22%). A further study was conducted with double dose of ISA 763 AVG, which led to an increased RPS value of 97.37%. Moreover, immunised cobia exhibited significantly greater lysozyme activity, antibody responses, and expression of certain immune-related genes post-challenge. Altogether, our results demonstrated that a combination of α-enolase recombinant protein with ISA 763 AVG adjuvant is a promising vaccine that can be employed for protection of cobia against S. dysgalactiae infection.

The feeding habits and growth of larvae and juveniles under artificial culture conditions were examined using the ecological method of simple random sampling to better understand the feeding characteristic of cobia (Rachycentron canadum) during the early development stage. The results showed that cobia larvae had a good foraging capability. After three days of the hatch (DAH), the larvae began feeding, and the feeding incidence was 70%. Feeding incidence was 100% in the case of juveniles. Feed intake of larvae and juveniles increases with increased body mass and could be expressed using the binomial equation (R2 = 0.9188). The digestive tract fullness coefficient of 3–24-day-old larvae and juveniles fluctuated from 0.1% to 1.0%. The larvae and juveniles of cobia were satiated within 1 h. The digestion time of larvae to rotifers and copepods was between 0.5 and 1.5 h and 0.5–2 h, respectively, while that of juveniles was 1–3 h. The daily feeding rates of larvae and juveniles were 61.38% (5-day-old), 54.18% (10-day-old), and 24.85% (24-day-old), and could be used as a reference for the daily feeding (%) of both larval and juvenile stages of cobia. The feeding patterns of larvae and juveniles showed a circadian rhythm, suggesting that they were fed during the day. The average daily growth rate of full-length larvae and juveniles aged 3 to 24 days was 35.90%, with an average daily weight gain rate of 56.97%. The relationship among total length, body mass, and age were expressed using a quadratic equation of one variable (R2 > 0.90) and a power function (R2 > 0.90) for the regression equation of body mass and full length. This study provides useful insights on the early development stage, and a reference for large-scale production of cobia larvae and juveniles.

Hypoxia is one of the most frequently arising stressors in aquaculture. Hypoxia causes huge financial losses and degradation of resources. However, the response of cobia (Rachycentron canadum) to hypoxia stress is not completely understood. In this study, the effects of hypoxia on the intestinal microflora of juvenile cobia were investigated. The diversity and structure of microflora after 4 weeks of hypoxia stress were analyzed using high-throughput sequencing technology. A total of 210 fish were divided into two treatment groups, namely, hypoxic stress and normoxic control groups, with 3 replicates per group and 35 fish per replicate. The results showed that the richness and diversity of intestinal microflora increased significantly first and subsequently decreased significantly after invitation of the hypoxia stress (P

This experiment was conducted to study the effect of various dietary alanyl-glutamine dipeptide (AGD) and/or vitamin E (VE) supplement(s) on the expression of glutathione peroxidase (GPx) and peroxisome proliferator-activated receptor α (PPARα) genes, antioxidation, feed utilization, growth, and composition of juvenile cobia (Rachycentron canadum). Six groups of the juveniles in triplicate were fed for 12 weeks using 6 diets: Control diet (D0) contained only basic ingredients; Diet 1 (D1) contained single added AGD 10 g kg− 1 dried feed; Diet 2 (D2) contained single added VE 100 IU kg− 1 dried feed; Diet 3 (D3) contained added AGD 10 g kg− 1 dried feed and VE 100 IU kg− 1 dried feed; Diet 4 (D4) contained added AGD 5 g kg− 1 dried feed and VE 50 IU kg− 1 dried feed; Diet 5 (D5) contained added AGD 2.5 g kg− 1 dried feed and VE 25 IU kg− 1 dried feed. The juveniles were sampled randomly for analysis in week 0 and week 12. The main results were as follows: the diets with combined AGD and VE supplements could considerably promote feed utilization, growth, and improve composition of the juveniles; the combined AGD and VE supplements could significantly promote (P

This experiment evaluated the efficacy of benzocaine to reduce stress response during transport of juvenile cobia. Fish (30 g) were packed in bags and transported for 8 h (stocking density = 10 g L-1). Three concentrations of benzocaine were evaluated: 0, 2, and 6 mg L-1. Blood samples were taken for glucose and hematocrit before transportation, and then at 0, 2, 24, and 48 h after. Water quality parameters were verified. No mortality was observed. Total ammonia nitrogen was higher (2.46 mg L-1) and pH was lower (6.92) at 2 mg benzocaine L-1. There was an increase in blood glucose for all treatments on arrival, and it was higher for those exposed to benzocaine at 6 mg L-1, although at 48 h they were all similar. The hematocrit did not differ among treatments. The results suggest: 1) the density 10 g L-1 is considered safe for juvenile cobia transport; 2) benzocaine did not mitigate stress response on cobia during transport, therefore its use is not recommended for this purpose.

The growth of three cohorts of captive reared cobia, grown in a combination of flow-though and recirculating aquaculture systems, was progressively measured to determine the existence and extent of sexually dimorphic growth in cobia. Approximately 100 fish from each cohort were individually identified and regularly weighed until the average weight of the fish was approximately 5 kg. The sex of individuals was determined through gonadal observations at the conclusion of each trial and the gender fitted retrospectively to the growth data set. Intersex gonads were observed in the first two cohorts of cobia, with 16.9% incidence in cohort 1 and 6.8% in cohort 2. Cobia is considered a gonochoristic species. This was the first reported observation of intersex gonads in cobia and the first reported occurrence of intersex gonads from a gonochoristic fish species from Australian waters. Only one fish out of the 182 examined in the third cohort was identified as intersex. There was no sexually dimorphic growth in cobia when there was a relatively high incidence of the intersex anomaly, as seen in the first two cohorts of fish. In the relative absence of the intersex condition, female cobia was significantly larger than males from 2 kg onwards. The weight of female cobia was almost 30% more than that of males at 17 months of age when average weight of the cohort was 4.6 kg. It is likely that the first two cobia cohorts were exposed to endocrine disruption in some form, and the possible sources are discussed. Statement of relevance This study demonstrated that female cobia grow significantly faster than male fish and that investigations into monosex culture could lead to significant productivity gains for cobia aquaculture. It also demonstrated that cohorts containing intersex fish did not exhibit sexually dimorphic growth. It is likely that the reproductive anomaly is the result of disruption to the endocrine system.

We herein diagnose blood fluke (Digenea: Aporocotylidae) infections in sea cage-reared cobia (Rachycentron canadum) from Nha Trang Bay, Vietnam, using morphology, nucleotide sequences, scanning electron microscopy, and histopathology. This is the first report of this blood fluke beyond the Gulf of Mexico and contributes to our understanding of the disease implications of aporocotylid infections among marine aquacultured fishes. Blood flukes were morphologically identified as Psettarium cf. anthicum by having the combination of an extremely elongate body with rows of straight, ventrolateral tegumental spines and a sinistral posterolateral protuberance, an H-shaped intestine with asymmetrical posterior ceca, a lobed ovary, an ootype posterior to the male genital pore, and an extensively convoluted uterus located between the ovary and ootype. A comparison of the large subunit ribosomal DNA (28S), small subunit ribosomal DNA (18S), and internal transcribed spacer 2 (ITS2) derived from blood flukes infecting cobias in Nha Trang Bay and Gulf of Mexico revealed 5 (99.5% similarity in 28S), 3 (99.8%, 18S), and 12 (98.9%, ITS2) nucleotide differences between the geographic isolates. Adult blood flukes pierced the endocardium and penetrated the spongy myocardium or lesioned endocardium of the cobias from Nha Trang Bay. The associated heart lesion comprised fibro-granulomatous endocarditis with accompanying endocardial thrombi, including focal effacement of the endocardium adjacent to thrombi, hyperplasia of endocardial cells yielding a thickened endocardium within which adult flukes resided or fluke remnants were located, clusters of large epitheliod granulomas within thrombi and within the basal endocardium, and minute granulomas in spongy myocardium enclosing probable blood fluke eggs. These pathological alterations suggested that heavily-infected cobia may suffer reduced cardiac output via thrombi blocking normal blood flow and emboli causing infarcts. Acute mortality may be likely for heavily-infected cobias during periods of high cardiac output, e.g., during feeding in a sea cage, if concomitant with, or resulting in, circulation of emboli. The lesioned endocardium may reduce efficiency of respiratory gas exchange to cardiac myocytes as well as impair endocardial cell immune function.

This study investigated the effects of orally administered Plantago asiatica , Houttuynia cordata , and Mentha haplocalyx on the growth and nonspecific immune responses of cobia ( Rachycentron canadum ). The nonspecific immune parameters assessed were weight gain, feed conversion ratio, superoxide anion (O 2 − ) production, superoxide dismutase (SOD) activity, phagocytic rate, phagocytic index, lysozyme activity, serum albumin and globulin, and albumin:globulin (A/G) ratio. The growth experiment indicated that 6-week dietary treatments did not significantly affect on the growth of cobia. Nonspecific immune responses showed that O 2 − production, SOD and lysozyme activity, and phagocytosis were significantly increased after the oral administration of P. asiatica and H. cordata , and the serum albumin:globulin ratio (A/G) gradually decreased. In this study, treatment of the Mentha haplocalyx on the cobia didn't present with the inducing of the phagocytosis ability compared with the treatment of P. asiatica and H. cordata. We suggest that oral administration of the 10 g/kg or 20 g/kg of the P. asiatica and H. cordata is exactly inducing the phagocytosis, ROS production, lysozyme activity and SOD production in the cobia.

Cobia (Rachycentron canadum) has been considered as a potential species for aquaculture because of its fast growth and commercial value. As a consequence of successful spawning and seed production, there has been a significant demand for cage farming of cobia in India (Philipose et al. 2013). Not many reports are available on diseases of cage-farmed cobia. Globally, mortality due to pasteurellosis in cage-cultured cobia caused by Photobacterium damselae subsp. piscicida has been reported (Liu, Lin & Lee 2003). Vibriosis caused by Vibrio alginolyticus, V. harveyi, V. parahemolyticus and V. vulnificus has also been responsible for mortalities in cage-cultured cobia (Rajan et al. 2001; Liu et al. 2004). Photobacterium damselae subsp. damselae was originally isolated from the skin lesions of damsel fish, Chromis punctipinnis (Love et al. 1981). Subsequently, diseases caused by this pathogen have been reported in several cultivable fish species like seabream (Vera, Navas & Fouz 1991), eel (Ketterer & Eaves 1992), turbot (Fouz et al. 1992), ovate pompano (Zhao et al. 2009) and Asian seabass (Kanchanopas-Barnette et al. 2009). Infection caused by P. damselae subsp. damselae has also been recorded in marine mammals like dolphins (Fujioka et al. 1988) and several wild fish species (Han et al. 2009). Pathogenicity of this bacterium in several marine fish species and humans has been reviewed (Rivas, Lemos & Osorio 2013a). There have been no reports on mortality caused by this pathogen in cobia. This study was envisaged with the objectives to describe the disease epizootic caused by P. damselae subsp. damselae in cage-farmed cobia and characterize the pathogen.

This study assessed the protein and energy requirements of Cobia (Rachycentron canadum) using a bio-energetic factorial approach. Using a series of inter-related studies, several parameters were defined to enable the construction of a bio-energetic factorial model for this species. The studies included two controlled laboratory experiments and also extensive field-data collection from commercial and research farms in Vietnam. The devised model includes parameters for both maintenance and protein demands; the effect of fish live-weight on maintenance protein (LW0.697), lipid (LW0.972), and energy demands (LW0.815); the efficiencies of protein, lipid and energy utilisation at various protein, lipid and energy intake levels; and the variability in whole body composition with varying live-weight. The protein utilisation efficiencies (0.456 · [protein intake] − 0.445), lipid utilisation efficiencies (1.292 · [lipid intake] − 1.120) and energy utilisation efficiencies (0.651 · [energy intake] − 48.41) were similar to other carnivorous fish species. However, the maintenance requirements for both energy (74.3 kJ/kgBW0.8/d− at 28 °C) and protein (0.99 g/kgBW0.7/d at 27.9 °C) were about double to other species. Using this modelling approach it was possible to iteratively derive optimal dietary protein and energy specifications for this species.